The invention relates to a method for operating a drive device with an internal combustion engine and with an exhaust gas system connected to the internal combustion system, which exhaust gas system has at least one catalytic converter to which a hot air stream which is heated by means of a heating device is supplied for heating. The invention also relates to a drive device.
The drive device serves for example for driving a motor vehicle. The drive device can be a part of a hybrid drive device, which beside the drive device has at least one further drive device, which for example has an electric machine in particular only the electric machine. Hereby it can be provided that the drive device and the further drive device, at least temporarily in cooperation, generate a torque for driving the motor vehicle. For this purpose the drive device and the further drive device are for example operatively connected with each other by means of a transmission. Beside the internal combustion engine, the drive device includes the exhaust gas system. The exhaust gas system serves for discharging the exhaust gas generated by the internal combustion engine in the direction of the external environment of the drive device. In order to meet exhaust gas provisions it is required to at least partially purify the exhaust gas before it reaches the external environment. For this purpose the exhaust gas system has the catalytic converter. When passing through the exhaust gas system the exhaust gas of the internal combustion engine is conducted through the catalytic converter in which a catalytically favorable reaction, in particular a reduction, takes place. After passing through the catalytic converter the exhaust gas can be conducted into the external environment by the exhaust gas system.
The catalytic converter usually has to have a defined operating temperature, in order for the reaction to take place and for the purification of the exhaust gas to be performed. The catalytic converter is heated on one hand by way of the exhaust gas which flows through the catalytic converter and which downstream of the internal combustion engine has a high temperature. In particular at low external temperatures and/or a cold start of the drive device, however, the time period that passes until the catalytic converter reaches the operating temperature, may be relatively long. In this time period the reaction cannot occur or can only occur at low efficiency so that the exhaust gas is not reliably or not completely purified.
This problem is particularly pronounced in the hybrid drive device because in this case the internal combustion engine is not constantly in operation. This means that in time periods in which only the further drive device is operated for providing a torque, while the drive device and with this the internal combustion engine is deactivated, the catalytic converter is not heated by the exhaust gas. Correspondingly its temperature decreases. When the temperature falls below the operating temperature, the exhaust gas generated when reactivating the drive device or the internal combustion engine cannot reliably be purified.
For this reason the heating device is provided by means of which the hot air stream is generated and subsequently supplied to the catalytic converter in the at least one operating state of the internal combustion engine for heating the catalytic converter. As a result of operating the heating device, the catalytic converter can thus be maintained at or above its operating temperature also during time periods in which the internal combustion engine is not operated or in which it is deactivated. The heating device is in particular provided in internal combustion engines that are constructed as diesel internal combustion engines. According to the above, the catalytic converter can be heated directly by means of the heating device. This means that the heating device is not or at least not only connected with the catalytic converter in heat transfer connection via a thermally conducting connection. Rather, a fluid for generating the hot air stream is heated and subsequently the catalytic converter is heated by means of the hot air stream.
The temperature that can be achieved by means of the heating device is usually very high and—at least immediately downstream of the heating device—is above the maximally permissible temperature of the catalytic converter. For this reason it can be provided that the heating device for generating the hot air steam is only operated during operation of the internal combustion engine and to mix the hot air stream into the exhaust gas of the internal combustion engine upstream of the catalytic converter. The exhaust gas usually has a temperature that is lower than the temperature of the hot air stream. In the case of a sufficient exhaust gas stream the temperature of the fluid, which flows through the catalytic converter and is composed of the hot air stream and the exhaust gas of the internal combustion engine, is thus sufficiently low and preferably corresponds to at least the operating temperature, however, it is lower than the maximally permissible temperature of the catalytic converter.
However, when the exhaust gas stream is too low, for example because the internal combustion engine is deactivated, the temperature of the hot air stream at optimal efficiency of the heating device is too high. Therefore it can be provided to decrease the efficiency of the heating device to lower the temperature to a degree that is appropriate for the catalytic converter. Such a lowering of the efficiency, however, means that the potential of the heating device is not fully realized and in addition the amount of generated pollutants is greater compared to an operation with optimal efficiency.
From the state of the art for example the printed publications DE 43 20 880 A1 and DE 44 10 820 A1 are known. The former relates to a control device for introducing air into an exhaust gas line of an internal combustion engine. Hereby it is provided to operate a heating device when a start switch is activated. In addition air is to be introduced into an air intake line during and after the start of the internal combustion engine, however, a control valve is not to be open during a predetermined time period T1 after switching on the star switch. The latter printed publication discloses an additional air supply device for an internal combustion engine and a gas heating device for the air supply device.